Method of manufacturing a rotor assembly

ABSTRACT

A method and apparatus for making a rotor assembly for an electric motor wherein the motor core of the assembly includes a stack of annular laminations having fixed molded annular end rings on opposed faces thereof with a rotor shaft extending through the core and fixed thereto by a molded rotor hub shaped in cup-like fashion at one end thereof to cooperate in forming an oil return member therewith.

BACKGROUND OF THE INVENTION

The present invention relates to a method of manufacturing a rotorassembly for an electric motor and an improved rotor assembly whichincludes a novel molded rotor core and a novel manner of molding andassembling such rotor core with a rotor shaft extending therethrough,including a unique arrangement for an oil return tube.

As is set forth in both prior coassigned U.S. Pat. Nos. 4,209,722, and4,499,661, both issued to C. Theodore Peachee, Jr., on June 24, 1980,and Feb. 15, 1985, respectively, in certain dynamoelectric machines ofthe induction motor type, and particularly in many smaller motorssometimes referred to as unit bearing motors, the motors have a squirrelcage rotor assembly in which the conductor bars for the rotor and theend rings of the rotor are made of die cast aluminum. Typically, theserotor assemblies include a stack or rotor core of individual laminationsconstructed from suitable ferro-magnetic material. Each lamination has acentral opening and a plurality of satellite openings or slots adjacentits outer margin. The laminations are assembled in a stack and thelaminations are rotated slightly with respect to one another in thestack so that their central openings are coaxial but so that their slotsare skewed relative to one another and so that the slots constitutepassages. The lamination stack or core is then placed in a suitable diecasting mold and molten aluminum is injected under pressure into themold to fill the mold, to flow through the skewed passages in the coreformed by the slots so as to form the conductor bars of the rotor and toform the rotor end rings. These die cast squirrel cage rotors typicallyhave a central opening therethrough and a rotor shaft extending throughthis opening which is rigidly secured to the rotor so that the shaftrotates with the rotor. This central opening may be defined at least inpart by the central opening of the laminations and is appreciably largerthan the shaft so as to receive a rigid boss of the motor housing. Therotor shaft is received in an opening in the boss and is journalledtherein by a suitable journal bearing or the like so as to rotatablysupport the rotor on the motor housing. As is typical, a portion of therotor shaft journalled in the bearing has a helical oil groove formed onits outer surface and the outer end of the shaft rotates in a felt wicksupplied with lubricating oil from a reservoir. Upon rotation of therotor, the oil grooves in the shaft pick up oil from the wick and moveit along the length of the bearing to lubricate it. Upon the oil beingdischarged from the inner end of the bearing, it is slung outwardly bythe centrifugal force of the rotating rotor shaft.

In prior art motors having such rotors, a return system was provided forrecirculating the oil to the oil supply reservoir. This oil returnsystem typically included a tubular oil return member which was fittedinto the opening in the rotor after die casting. This oil return membersurrounded the bearing boss and extended out beyond the end of therotor. The inner end of this oil return member was sealed to the rotorbody by application of a sealant. An outer end cap carried by the motorhousing surrounded the outer end of the oil return member and collectedoil which flowed out of the end of the oil return member from the insideof the rotor.

In the manufacture of these prior art die cast squirrel cage rotors, ithas heretofore been difficult to fit the oil return member into therotor body and to seal the inner end of the oil return member to therotor body. As mentioned above, the sealing operation usually involvedthe application of a sealant to the joint between the inner end of theoil return member and the rotor body. However, many of the motors whichincorporated these die cast squirrel cage rotors were relatively smalland the space in which the sealant had to be applied was cramped. Also,the application of sealant was a messy and time-consuming operationperformed after die casting of the rotor thus resulting in increasedlabor costs for the manufacture of the motor.

In prior coassigned U.S. Pat. No. 4,209,722, a die cast rotor isdisclosed in which a tubular oil return member is sealably diecast-in-place within the rotor body. However, this die cast-in-place oilreturn member was separate and apart from a securement member which wasalso die cast-in-place within the rotor body, this securement memberreceiving and rigidly securing the rotor shaft to the rotor body.Typically, this rotor shaft securement member was made of brass. Duringdie casting of the rotor, it was necessary to separately locate or placeboth the oil return tube and the rotor shaft securement member in thedie cavity of the die casting machine. The placement of these two partsrequired a certain degree of skill and time on the part of the operatorof the die casting machine.

In prior coassigned later U.S. Pat. No. 4,499,661, the oil return tubeand rotor shaft mounting member are integrally formed as one piece bycold extrusion and inserted within the central opening of a rotor coreincluding a lamination stack. Molten metal is then die cast around theone piece oil return and rotor shaft mounting member and around thecore, and the rotor shaft is then fixedly secured to the rotor shaftmounting member of the extruded integral piece. This later U.S. Pat. No.4,499,661 enhanced rotor assembly over the previous teachings in theart, eliminating assembly parts with the oil return tube serving as alocater for the rotor core in assembly operations, providing aneconomical way to manufacture the rotor assembly with reduced scrap andwith reliable operation.

The present invention provides a new and useful method of manufactureand a unique structural rotor assembly which can be produced by an evenmore straightforward and efficient series of manufacturing steps, andwhich provides a rotor assembly of even greater reliability inoperation, further extending the life of the motor in which it isemployed. In this regard, the present invention provides a novel methodand rotor assembly arrangement which provides for an optimization ofresistance control in the rotor assembly with a minimum of moltenmaterials through a comparatively simple, straightforward series ofmanufacturing steps, including a unique, straightforward assembly stepwith respect to the oil return tube and which, at the same time,provides for efficient oil distribution operations with a tight sealbetween the several parts of the assembly. In addition, the uniquemethod and apparatus of the present invention, recognizing theundesirability of oil losses, minimizes the porosity of those partswhich are contacted with oil and, at the same time, ensures effectiverecycling of such oil with a minimum of sealing parts. Further, thepresent invention permits for a reduction in costly secondary machiningoperation and also allows for the selective scrapping of parts whichmight appear to be defective during manufacturing quality inspectionprocedures.

Various other advantageous features of the present invention will becomeobvious to one skilled in the art upon reading the disclosure set forthherein.

SUMMARY OF THE INVENTION

More particularly, the present invention provides an improved rotorassembly arrangement for an electric motor comprising: a rotor coreincluding a stack of annular laminations of suitable ferro-magneticmaterials with annular end rings in fixed molded relation with opposedfaces of the stack of annular laminations to define a longitudinallyextending rotor core opening therethrough and provide a longitudinalaxis of rotation about which the rotor core is rotatable; a rotor shaftextending through the rotor core opening along the longitudinal axis ofrotation; a rotor hub molded within the rotor core opening in fixedrelation to the stack of annular laminations and the rotor shaft withone end of the molded rotor hub having a cup-like opening therein withthe base of the cup-like opening being molded in fast relation aroundthe rotor shaft; and, a tubular open-ended oil return membercooperatively disposed relative and in alignment with the cup-likeopening in the rotor hub to surround the rotor shaft in spaced relationthereto. In addition, the present invention provides a unique oil returntube or cap arrangement which can be either integrally molded as part ofthe cup-like opening in the rotor hub or can be formed from a non-porousmaterial such as a high modulus plastic sized and shaped to be press-fitinto nesting, sealed relation with the cup-like opening of the rotor huband surrounding the rotor shaft. Further, the present invention providesfor a molded rotor hub arrangement which allows for an end of the rotorshaft to be embedded therein or alternatively to project therethrough.Further, the present invention provides a unique and novel method ofmanufacturing a rotor assembly for an electric motor such as one likethe unique rotor assembly above described including the steps of formingthe rotor core by molding annular end rings along opposed faces of thestack of annular laminations; inserting and supporting the shaft inconcentrically spaced relation from the inner peripheral wall of thestack of annular laminations so that the longitudinal axis of the shaftextends along the central axis of rotation of the rotor assembly;molding a rotor hub between such inner peripheral wall of the stack ofannular laminations and the concentrically supported rotor shaft to fixthe rotor core to lamination stack and the rotor shaft, the rotor hubbeing molded to include a cup-like opening with the mouth therefore atone end thereof for concentric cooperative relation with an oil returntube; and, forming such oil return tube or cap sized and configured tobe in such concentric cooperation with the cup-like opening formed inthe rotor hub.

It is to be understood that various changes can be made by one skilledin the art in one or more of the several steps of the inventive methoddescribed herein and in one or more of the several parts of the novelstructure disclosed herein without departing from the scope or spirit ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings which disclose an advantageous embodiment ofthe inventive rotor assembly arrangement, a modification thereof, and aschematic flow diagram of the inventive method:

FIGS. 1a through 1c are exploded views partially in cross section, ofthe inventive rotor shaft, oil return tube and rotor core;

FIG. 2 is an assembled cross-sectional side view of the rotor assemblyincluding the several parts of FIG. 1 and a rotor hub extending betweenthe rotor core and rotor shaft;

FIG. 3 is an assembled cross-sectional side view, similar to the view ofFIG. 2, of a modified rotor assembly disclosing a rotor shaft endembedded in the rotor hub which hub is provided with a threaded endprotrusion aligned with the rotor shaft axis;

FIG. 4 is a cross-sectional side view of a motor incorporating the rotorassembly of FIG. 2; and,

FIG. 5 is a schematic flow diagram setting forth the several steps ofthe inventive method.

DETAILED DESCRIPTION OF THE DRAWINGS

As can be seen in FIGS. 1 and 2 of the drawings, the inventive rotorassembly 2 shown in the assembled arrangement in FIG. 2 comprises arotor core 3, a rotor shaft 4, a rotor hub 6 (FIG. 2) and a tubularopen-ended oil return member 7, the shaft 4, oil return member 7 and arotor core 3 being shown in exploded, unassembled form in FIG. 1.

As can be seen in the drawings, rotor core 3 includes a stack of annularlaminations 8 which can be punch-formed from sheets of suitableferro-magnetic material and assembled and joined in a manner asabove-described. Specifically, the punched laminations, each having acentral opening and a plurality of outer peripheral slots, are assembledin a stack and rotated slightly with respect to one another in the stackso that the central openings are coaxial to define an inner peripheralwall and the outer peripheral slots are skewed relative to one anotherto provide skewed passages in the core. Molded aluminum can then beinjected under pressure into the skewed passages to form the conductorbars of the rotor. Annular end rings 9 are fixed, advantageously by diecast molding, to the opposed faces of the stack of laminations 8. Theseannular end rings, like the conductor bars in the skewed peripheralpassages, can be die cast from aluminum, and are sized and shaped in apreselected manner relative to the stack of annular laminations 8 toprovide a preselected controlled rotor resistance with the stack ofannular laminations, the annular rings 9 and inner peripheral wall ofthe stack of annular laminations 8 defining a longitudinally extendingrotor core opening 11 therethrough to provide a longitudinal axis ofrotation 12 about which rotor assembly 2 can be rotated.

Rotor shaft 4, which can be cut and shaped from a suitable material suchas a bar stock of cold rolled steel, can be provided at one end portionthereof with a helical oil groove 13 and at the opposite end portionthereof with a threaded end 14. As is known in the art, a suitablelongitudinally extending undercut portion 16 can be provided on rotorshaft 4, intermediate helical groove 13 and threaded end 14. Rotor shaft4 is positioned within rotor core opening 11 to extend longitudinally inspaced relation through such rotor core opening with its longitudinalaxis defining the aforementioned rotor assembly axis of rotation 12.

As can be seen in FIG. 2 of the drawings, the rotor hub 6 is molded froma suitable material, such as die cast zinc or high modulus plasticwithin rotor core opening in fixed relation to the inner peripheral wallof the rotor core 4 defined by the stack of annular laminations 8 andthe outer periphery of rotor shaft 4. As will be noted in FIG. 2,threaded end 14 of rotor shaft 4 can be arranged to extend beyond moldedrotor hub 6 to engage in male-female relation with a central aperture ina fan blade to be mounted on the threaded end 14 with an internallythreaded nut (not shown). The opposite end of molded rotor hub 6 isprovided with a cup-like opening in the form of a substantiallycylindrical open-ended passage 17 with the base molded in fast relationaround the outer periphery of rotor shaft 4 as above discussed.

Tubular open-ended oil return member 7 can be cooperatively disposedrelative and in alignment with cup-like opening 17 in rotor hub 6 tosurround the rotor shaft in spaced concentric relation therewith.

As disclosed in FIGS. 1 and 2 of the drawings, oil return member 7 canbe formed separately in unitary fashion from a suitable non-porousmaterial, such as a high modulus plastic, to include a tapered mouthportion 18 which tapers inwardly from the open end thereof to asubstantially cylindrical body portion 19 which includes an aperturedbase 21. The cylindrical body portion 19 with its apertured base 21 iscross-sectionally and longitudinally sized to snugly nest withopen-ended cylindrical passage 17, with apertured base 21 snuglyembracing the outer periphery of rotor shaft 4 and abutting the base ofcylindrical passage 17 in rotor hub 6 when tubular oil return member 7is press-fit therein. In this regard, it is to be noted that cylindricalbody portion 19 and apertured base 21 of oil return member 7 can be ofsufficient length and breadth respectively to ensure projection oftapered mouth portion 18 beyond the open-ended mouth of the cup-likecylindrical passage 17 in rotor hub 6.

It is to be understood, as shown in FIG. 3 of the drawings, that rotorshaft 4 can be embedded in molded rotor hub 6 with hub 6 being so moldedas to include an externally male threaded projection 22 in alignmentwith rotor shaft 4 to receive the central aperture of a fan blade (notshown) and an internally threaded nut for mounting and retaining suchblade. It is further to be understood that it also would be possible inaccordance with the present invention to mold tubular oil return member7 as an integral part of rotor hub 6. In such event, it only would benecessary to provide a tapered mouth portion substantially of theconfiguration of mouth portion 18 only extending outwardly from theouter periphery of the mouth of cylindrical opening 17 in rotor hub 6.

Referring to FIG. 4 of the drawings, the inventive rotor assembly 2 isdisclosed with the rotor shaft 4 in engagement with a central bearingboss 23 extending inwardly from motor 24. Boss 23 is rigid and serves asa support for shaft 4 to provide the unit bearing motor 24, the boss 23and outer housing 26 thereof being of a suitably molded configurationsimilar to the motor arrangement in aforediscussed U.S. Pat. No.4,209,722. Accordingly, functional details of storage wick 27, cap 28,push nut 29 on rotor shaft 4, and washer wick 31 are not fully describedherein. It is to be noted, however, that due to the unique press-fit orintegral relation of the oil return tube 7, the thrust washer and spacerwasher which had been required with the rotor hubs in previous rotorassemblies have now been eliminated, reducing material and assemblycosts and simplifying motor operations.

Referring to FIG. 5 of the drawings, a schematic diagram of theinventive method steps is disclosed. This method includes the steps offorming a rotor core 3 by punching a plurality of annular laminationsfrom a sheet of suitable ferro-magnetic material with each laminationhaving a central opening and a plurality of outer slots. The annularlaminations are then assembled in a stack so that the central openingsare coaxial to define an inner peripheral wall surrounding rotor coreopening 11, and the outer peripheral slots are skewed to provide skewedpassages. With the laminations supported in this manner as a stack oflaminations 8, the skewed passages are die cast with molten aluminumunder pressure to form the conductor bars in the lamination stack 8 ofrotor core 3 along with a pair of annular rings 9 sized and shaped in apreselected form, advantageously of trapezoidal cross-section, beingthen die cast simultaneously from such molten aluminum under pressure onopposite faces of the stack. These annular rings 9 are of preselectedsize and shape to control resistance in the rotor core 3. The rotor core3 then is appropriately ground to desired tolerance, removing burrs andedges from the core. Substantially, at the same time that core 3 isformed in the manner described, rotor shaft 4 can be cut and shaped fromselected bar stock material, such as cold rolled steel, to include anintermediate undercut section 16. The shaft is then rough ground androlled to include at one end portion thereof along the outer peripherythereof a helical oil groove 13 to extend from one extremity thereof tothe undercut section or portion 16 and an externally threaded portion 14is rolled at the opposite extremity of shaft 4.

The shaped and rolled shaft 4 can then be inserted and supported throughcentral opening 11 defined by the inner peripheral wall of the stack ofannular laminations 8 so as to be in concentrically spaced relation fromsuch wall within the longitudinal axis of shaft 4 defining and extendingalong the central axis of rotation of rotor core 3.

Rotor hub 6 is then die cast under suitable pressure from an appropriatezinc or high modulus plastic material to extend between the innerperipheral wall of the stack of annular laminations 8 and the peripheryof the concentrically supported rotor shaft 4. The threaded end 14 ofshaft 4 is arranged to extend externally from the die cast material toprovide a fan mount. In this regard, it is to be understood that suchend of rotor shaft 4 can be embedded in the rotor hub 6 and the rotorhub so die cast as to include a threaded external projection 15extending in axial alignment with shaft 4 to provide such fan mount(FIG. 3). It is to be noted that rotor hub 6 also is so die cast as toinclude a cup-like opening at the end thereof opposite the fan mount.This opening can be of substantially cylindrical shape to nestinglyreceive a portion of the oil return tube 7 therein.

The oil return tube 7, which can be formed from a suitable non-porous,high modulus plastic, is formed to include outwardly flanged mouthportion 18 and cylindrical body portion 19 terminating in an aperturedbase member 21. In forming tube 7, the tube portions are so sized alongtheir lengths and cross-sections that when tube 7 is press-fit into thecylindrical opening 17 of rotor hub 6 the cylindrical body portion 19sealingly nests therein with base 21 abutting the base of the cup-likeopening 17 and the aperture in base 21 snugly embracing rotor shaft 4with the shaft 4 extending in concentric relation with cylindrical bodyportion 19 of tubular oil return member 7 and flange or tapered mouthportion 18 concentrically surrounding helical groove 13 and adjacentundercut section 16 of shaft 4.

Thus, a novel, straightforward, economical and reliably operating rotorassembly structure can be formed by a novel method with a minimum ofcost, steps, and parts.

The invention claimed is:
 1. A method of manufacturing a rotor assemblyfor an electric motor, said rotor assembly having a central longitudinalaxis of rotation about which said assembly is rotated when installed insaid motor; said assembly including a rotor core having a stack ofannular laminations of suitable ferro-magnetic materials with an innerperipheral wall formed by said stack of annular laminations defining acentral opening therethrough about said central longitudinal axis, arotor shaft extending along said central longitudinal axis, a rotor hubbetween said core and shaft, said hub having a cup-like opening at oneend thereof, and an oil return tube extending coaxially with saidcentral longitudinal axis, said oil return tube being sized andconfigured to be in concentric, cooperating relationship, comprising thesteps of:forming said rotor core by molding a pair of annular end ringsalong opposed faces of said stack of annular laminations; inserting arotor shaft through the central opening defined by said stack of annularlaminations and supporting the shaft in concentrically spaced relationfrom said inner peripheral wall of said stack of annular laminations sothat the longitudinal axis of said shaft extends along said central axisof rotation; molding a rotor hub between said inner peripheral wall ofsaid stack of annular laminations and said concentrically supportedrotor shaft to fix said rotor core to said rotor shaft, said rotor hubbeing so molded to include said cup-like opening at one end thereof forconcentric cooperative relation with said oil return tube; and,providing said oil return tube in concentric, cooperative relation withsaid cup-like opening formed in said rotor hub.
 2. The method ofmanufacturing a rotor assembly of claim 1, forming said oil return tubeseparately from a non-porous material in open-ended cup-like form withan aperture in the base thereof, said tube being sized to snugly nest insealed engagement with said rotor shaft within said cup-like opening insaid rotor hub; and,press-fitting said oil return tube into such sealedengagement with said rotor hub cup-like opening and said rotor shaft. 3.The method of manufacturing a rotor assembly of claim 1, the step ofmolding the rotor hub including die casting with a zinc material.
 4. Themethod of manufacturing a rotor assembly of claim 1, the step of moldingthe rotor hub with a high modulus plastic material.
 5. The method ofmanufacturing a rotor assembly of claim 1, the step of molding the rotorhub including embedding one end of said rotor shaft entirely within saidmolded material; forming a molded protrusion at the extremity of saidmolded rotor hub material in alignment with the longitudinal axis ofsaid rotor shaft, said protrusion including external threads thereon forfan mounting.
 6. The method of manufacturing a rotor assembly of claim1, the step of molding the rotor hub including embedding a portion ofone extremity of said rotor shaft within said molded material with theend of said extremity of said rotor shaft protruding externally fromsaid molded material; and rolling external threads on said protrudingshaft end for fan mounting.
 7. The method of manufacturing a rotorassembly of claim 1, including the steps of rolling an oil groove at oneend of said rotor shaft and rolling threads at the opposite end of saidshaft prior to insertion and supporting within said central openingdefined by said annular laminations of said rotor core.
 8. The method ofmanufacturing a rotor assembly of claim 1, the step of forming saidrotor core further including the step of grinding said rotor core priorto installation and supporting said rotor shaft therein.
 9. A method ofmanufacturing a rotor assembly for an electric motor, said rotorassembly having a central longitudinal axis of rotation about which saidassembly is rotated when installed in said motor, said assemblyincluding a rotor core including a stack of annular laminations ofsuitable ferro-magnetic materials with an inner peripheral wall formedby said stack of annular laminations defining a central openingtherethrough about said central longitudinal axis, a rotor shaftextending along said central longitudinal axis, a rotor hub between saidcore and shaft and an oil return tube extending coaxially with saidcentral longitudinal axis comprising the steps of:forming said rotorcore by punching a plurality of annular laminations from a sheet ofsuitable ferro-magnetic material with each lamination having a centralopening and a plurality of outer peripheral satellite slots; assemblingsaid annular laminations in a stack so that the central openings arecoaxial to define an inner peripheral wall and the outer peripheralsatellite slots are skewed to provide skewed passages; die casting saidskewed passages to form the conductor bars of said rotor andsimultaneously die casting a pair of annular rings along opposed facesof said stack of laminations to form said rotor core, said pair of endrings being die cast from aluminum material and being sized andgeometrically shaped in preselected trapezoidal cross-section to providea controlled resistance for said rotor core; grinding said rotor core todesired tolerance and to remove burrs and edges thereon; cutting a rotorshaft from selected bar stock to include an undercut midsection andrough grinding the same; rolling said shaft to include a helical oilgroove extending from one end thereof to said undercut midsection and tofurther include a rolled threaded section at the opposite end thereof;inserting said rolled shaft through the central opening defined by saidstack of annular laminations and supporting said shaft in concentricallyspaced relation from said inner peripheral wall defined by said annularlaminations so that the longitudinal axis of said shaft extends alongsaid central axis of rotation of said rotor; die casting a rotor hubfrom zinc material to extend between said inner peripheral wall of saidstack of annular laminations and said concentrically supported rotorshaft with said rolled threaded end of said shaft extending externallyfrom said die cast material to provide a fan mount, said die cast rotorhub including a cup-like opening at one end thereof to nestingly receivea portion of an oil return tube therein; forming a non-porous plasticoil return tube to include an outwardly flanged mouth portion and acylindrical body portion terminating in an apertured base portion, saidoil return tube portions being preselectively sized along their lengthsand cross-sections in accordance with said cup-like opening in saidrotor hub; and, press-fitting said oil return tube into sealed relationwith said cup-like opening of said rotor hub and said rotor shaft sothat said cylindrical body portion snugly and sealingly nests in saidcup-like opening of said rotor hub with said base portion of saidcylindrical portion of said oil return tube abutting the base of saidcup-like opening and with said rotor shaft extending in sealed relationthrough said apertured base portion to be in spaced concentric relationwith said cylindrical body portion and said flanged mouth portion withsaid flanged mouth portion concentrically surrounding said rolledhelical oil groove and undercut intermediate section of said rotorshaft.